Tuner



M y 20, 1947- J. M. DODDS ET'AL 2,420,657

TUNER Filed Dec. 29, 1943 2 Sheets-Sheet 1 g mama bow.

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TUNER Filed" Dec. 29, 1943 2 Sheets-Sheet 2 UOH'M MATHlEso DODDSJML TOHN HElWOoD LWOLOW Patented May 20, 1947 TUNER John Mathieson Dodds, Timperley, and John Heywood Ludlow, Bowdon, England Application December 29, 1943, Serial No. 516,105 In Great Britain May 13, 1938 1 Claim.

This invention relates to radio transmitters of the kind in which provision is made for changing expeditiously the wavelength of transmission by the substitution of different tunin inductances the one for another. Such arrangements are mostly employed in transmitters operating on relatively short wavelengths such as in the range of from 13 to '70 metres which is used for beam working wherein owing to changes in conditions of propagation an alteration of wavelength is usually necessary to be effected frequently in order to ensure reasonable continuity of service.

In general, the wave changing arrangements comprise a number of inductances or tuned circuits mounted upon a rotating structure or turntable each inductance being provided with switch contacts so that any one of the inductances or tuned circuits can be connected to the associated power valve or valves. Such arrangement permits the change to be made in a relatively short time. Since on beam stations a separate aerial array is used for each wavelength, a selector switch has also to be operated to connect the appropriate feeder lines to the transmitter. In the use of such a rapid wave changing arrangement, having rotated the turntable to substitute one inductance or tuned circuit for another, the operator then sets the various variable tuning condensers to predetermined positions or values and causes the power to be applied, a final adjustment of the tuning condensers being usually necessary.

In our applications for Radio transmitters, Serial Nos. 516,103 and 516,104 filed of even date herewith are described particular forms of wave changing arrangements. The present invention concerns means whereby the tuning condenser may be rapidly and automatically adjusted simultaneously with the change of the connection of inductances to the valve electrode or electrodes.

The invention, however, is not limited in its application to transmitters having wave changing arrangements in accordance with the two applications just above mentioned. 7

Since it is in general difficult to provide for use on short wave circuits and relatively high power apparatus, an inductance coil the value of which can be varied in a continuous manner for tuning purposes, and even although the self-capacity of the valves is in general adequate for satisfactory operation without additional capacity, it is convenient to use variable condensers in combination with fixed inductances.

Where, in atransmitter havin wave changing arrangements, the appropriate inductance is selected by means of a switch or equivalent means, two arrangements for the tuning capacity may in general be employed. In one arrangement each inductance may be provided with its own variable condenser which is selected simultane ously with the inductance. In the other arrangement a single variable condenser is used in cooperation with whichever of the inductances is selected. The former arrangement has considerable advantage inasmuch as no readjustment of the tune is necessary after a wavelength change, apart from the final trimming. The arrangement thus permits wave changing to be effected with considerable rapidity, particularly when all the circuit switches are coupled for simultaneous operation throughout the transmitter. Unfortunately, however, the layout and design of such an arrangement becomes difficult, bulky and complicated owing to the large number of condensers involved. Consequently it is very diificult to achieve resonance at the very short wavelengths of say less than 10 metres.

The present invention provides meanswhereby the second arrangement above mentioned 0f having a single variable condenser can be effectively and expeditiously employed in connection with wavelength changing on a transmitter of relatively high power and very low wavelength.

To enable the invention to be clearly understood it will now :bedescribed by way of example with reference to the accompanying drawings, in Which Figures 1 and 2 are respectively an elevation and plan of one form of wave changing arrangement to which the present invention may. be applied.

Fig. 3 is an elevation of an apparatus for actuating the wave-changing arrangements of Figs. 1 and 2 in accordance with the invention, showing also how the condenser of the grid circuit as well as the condenser of the anode circuit of a valve or pair of valves may be concomitantly operated with the inductance changing switches in the anode and in the grid circuit of the valve, the operation being effected automatically under push-button control.

Referring to Figs. 1 and 2 of the drawings, I and 2 represent parts of the anodes of a pair of Valves operating in push-pull. To the anodes I and 2 are secured terminal members 3 which may be straps encircling the anodes. Each member 3 has hinged to its right-hand end a switch blade 4 which is adapted to engage any one of the fixed contact jaws 5, 6 and 1 by rotation of the shaft 8, which may be effected by any convenient u means. Each two corresponding jaw contacts 5, 6 and. I has connected to them an inductance coil 9, l and II respectively, these coils having different inductance values. The inductance changing arrangement just described per se forms the subject matter of the above mentioned application Serial No. 516,103. The terminal members 3 at their left-hand ends carry the fixed Plates l2 of a single or double variable condenser, the movable vanes [3 of which are adapted to be rotated by means of a shaft 14. It will be understood that, as hereinbefore set forth, the con denser I3 is required to be adjusted by rotation of the shaft M to have a preselected valu in accordance with which of the inductances 9, 18 or II is brought into circuit by means of the switch blades 4.

Referring now to Fig. 3, it is to be assumed that the shaft 8 in this figure is identical to the shaft 8 in Figs. 1 and 2 or is operatively connected with this latter shaft so that it operates the blades '4 for the purpose of selectively connecting, in this instance, four different inductances to the anodes of the push-pull valves. It is further to be assumed that the shaft 8a operates other switch blades for equivalently connecting four further inductances to the grids of said valves.

Secured to the shaft 8 is a disc or turntable 43 which carries four adjustable abutments each of which is in the form of a threaded rod 44 not rotatable but longitudinally slidable in a bracket '45 having two lugs between which is a worm wheel 46 having threaded engagement on the rod 44. This worm wheel 46 meshes with a worm 41 on a shaft 48 to which is secured a pinion '45. Another pinion 58 is carried at the end of a lever which is pivoted at 52 and is urged by a tension spring 53 so that it normally engages a fixed stop 54 so located that the pinions 49 and 50 are normally held a short distance but of mesh of each other. Rigid with the lever 5! is a hand lever 55 which may be pressed downwards so as to cause the pinions 49 and 58 to mesh with each other. On the shaft 56 of the pinion 58 is a hand wheel (not shown), whereby, when the lever '55 is pressed down, the pinions 50 and 49 may be rotated for the purpose of rapidly adjusting the abutment 44 as desired radially inwards and outwards with respect to the disc 43.

The roller 51 of the abutment 44 co-operates with a horn-shaped cam member 58 which is carried upon pivoted parallel links 59 and 68. The cam member 58 is normally urged towards the shaft 8 of the disc 43 by means of a spring BI connected to a fixed point 82 and to the lever 59. It will be seen in Fig. 3 that the roller 51 of the abutment 44 is in engagement with the short flat central portion 53 of the cam member 58, this central portion 63 being symmetrical with respect to the curved slopin away surfaces 84, The cam plate 58 has been pushed by the roller 51 away from the shaft 8 of the disc or turntable '43 to an operative position which corresponds to the position wherein the anode inductance selector switch blades 4 (Fig. 1) are properly mated with the fixed inductance contact jaws of the inductance which it is desired to use for a transmission on a particular predetermined wavelength. The lever 88 has pivotally connected to it a link 65 which is adapted to operate by any convenient means (not shown) the shaft l4 (Figs. land -2) of 'the anode tuning condenser l2, l3,

Assuming now that the shaft 8 is rotated in the clockwise direction the abutment roller 51 will pass down the left hand sloping portion 64 of the cam 58 allowing the latter to be pulled by the spring 6| towards the shaft 8. However, in the meantime the rolle 5! of the next abutment 44 engages somewhere on the outer part of the right-hand sloping portion 64 of the cam 58 and gradually pushes the latter away from the shaft 8 so as to set the anode tuning condenser to a new value of capacity which has been predetermined for the new Wavelength which is set up with another inductance when said roller 51 is in engagement with the short flat cam surfaceportion 83.

By further rotation of the shaft 8 the next abutment roller 51 and finally the roller of the fourth abutment engage successively the cam member 58 and thereby cause automatically the setting of the anode tuning condenser to particular capacity values which are predetermined with respect to the other inductance coils which have been switched into circuit by the blade 4 (Fig. 1). The disc 43 can be rotated in the reverse direction when desired.

The grid circuit wave changing of the valve is dealt with in a similar way by similar arrangements, the numerals of which are the same for similar parts but each has the sumx a so that a description of the grid circuit arrangement is considered unnecessary beyond stating that the disc 430, which carries the adjustable abutments 44a is driven from the disc 43 by means of a sprocket chain 431) or in any other convenient manner. It will be appreciated that owing to the lower voltage in the grid circuit the components in the grid compartment or chamber will occupy less volumetric space than is the case with the components in the anode compartment or chamber, and moreover the arc of action of the grid inductance changing switch arms will be less than that of the anode inductance changing switch arms so that the shaft 430 is geared down from the shaft '8.

It should be appreciated also that whilst in the arrangement shown in Fig. 3 the grid circuit abutr'nents 51a are carried n a sector 43d secured to the shaft 430, the group of abutments 5m may alternatively be mounted on the disc 43 opposite the group of abutments 5'! thereon. This will be advantageous in helping to balance the disc 43 since otherwise it is necessary or desirable to attach a weight or weights to the disc 43 to counterbalance the weight of the group of abutments 5'5 thereon.

In order that the system shownin Fig. 3 may be operated automatically under push-button control there are distributed around the disc limit switches 66 corresponding in number and position with the abut-merits '44. Each limit switch has a pivoted arm 61 which is normally biased by means of a spring so that it normally extends at an angle on either side of any radius passing from'the axis of the shaft 8 to the pivot of the arm 61. in the limit switch 65. The arms 6 are provided with forked ends 88 which are adapted to be engaged in succession by a pin 69 fi xed on the disc 43 when the latter is rotated in either direction. It will be noticed that the pin 69 has brought the pivoted arm '61 of one of the limit switches 66 into the radial position with respect to the axis of the shaft 8 and in this position the rotation of a reversible electric motor (not shown) which drives the discs 43 and 4312 has been stopped, the electrical supply to the motor having been previously initiated by the depression of an appropriate one: of a plurality of push-button switches. By the depression of another selected push-button switch the motor may be started again to cause the disc 43 to rotate until the next roller 51 of the abutment engages with the flat portion 63 of the cam member 58. By a suitable combination of push-buttons and control circuits the disc 43 may be caused to rotate expeditiously thereto, for instance to the shaft 8 so that all the components may be driven from one or more electric motors under the control of one set of push-buttons which may be located on a control desk along with the usual instruments and meters and other control devices.

It will be appreciated also that the wavelength may be changed when any selected inductance coil is in circuit, by pressing the lever 55 and rotating the hand wheel keyed to the shaft of the pinion 59.

It is further to be appreciated that the arrangements in accordance with the invention permit the wavelength of a transmitter to be changed very rapidly in comparison with the arrangements which have heretofore been employed and this is of great significance when taking into account the very short wavelengths involved.

We claim: e

In an apparatus of the character described, a rotatable shaft, a plurality of inductances positioned about said shaft, switch means fixed to said shaft and adapted to be rotated with the latter into selective engagement with the inductances, a plurality of abutments extending radially from said shaft and by different radial distances, a pivotally mounted. cam positioned in the path of movement of said abutments with said shaft, said cam including a central apex extending toward said shaft, and a variable condenser having its movable element operatively connected to said cam whereby the po-sitionof the movable element of the condenser will be determined by rotation of said abutments with said shaft.

JOHN MATHIESON DODDS.

JOHN HEYWOOD LUDLO-W.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,085,838 Usselman July 6, 1937 2,186,068 Hammond et al. 1 Jan. 9, 1940 1,581,145 Vasselli Apr. 20, 1926 1,727,575 Trogner Sept. 10, 1929 1,863,050 Hotopp, Jr June 14, 1932 1,965,281 Deisch 1- July 3, 1934 2,103,035 Lear Dec. 21, 1937 2,113,157 Landon et al. Apr. 5, 1938 2,115,619 Carpenter Apr. 26, 1938 2,278,371 Guy Mar. 31, 1942 1,684,519 Scheerbarth Sept. 18, 1928 1,809,932 Gebhard June 16, 1931 1,394,555 Ide Oct. 25, 1921 2,385,131 Garthwaite Sept. 18, 1945 2,078,909 Gunther Apr. 27, 1937 1,823,177 Trogner Sept. 15, 1931 1,984,301 Gebhard et al 1 Dec. 11, 1934 

